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In the last decade, the development of customized biodegradable scaffolds and implants has attracted increased scientific interest due to the fact that additive manufacturing technologies allow for the rapid production of implants with high geometric complexity constructed via commercial biodegradable polymers. In this study, innovative designs of tibial scaffold in form of bone-brick configuration were developed to fill the bone gap utilizing advanced architected materials and bio-inspired diffusion canals. The architected materials and canals provide high porosity, as well as a high surface area to volume ratio in the scaffold facilitating that way in the tissue regeneration process and in withstanding the applied external loads. The cellular structures applied in this work were the Schwarz Diamond (SD) and a hybrid SD&FCC hybrid cellular material, which is a completely new architected material that derived from the combination of SD and Face Centered Cubic (FCC) structures. These designs were additively manufactured utilizing two biodegradable materials namely Polylactic acid (PLA) and Polycaprolactone (PCL), using the Fused Filament Fabrication (FFF) technique, in order to avoid the surgery, for the scaffold's removal after the bone regeneration. Furthermore, the additively manufactured scaffolds were examined in terms of compatibility and assembly with the bone's physical model, as well as, in terms of mechanical behavior under realistic static loads. In addition, non-linear finite element models (FEMs) were developed based on the experimental data to accurately simulate the mechanical response of the examined scaffolds. The Finite Element Analysis (FEA) results were compared with the experimental response and afterwards the stress concentration regions were observed and identified. Τhe proposed design of scaffold with SD&FCC lattice structure made of PLA material with a relative density of 20% revealed the best overall performance, showing that it is the most suitable candidate for further investigation (in-vivo test, clinical trials, etc.) and commercialization. [Display omitted] [ABSTRACT FROM AUTHOR]

Methods for inspecting coating mechanical properties and adhesion on final products, considering quantitative criteria are of high importance. In this paper, relevant characteristic examples for determining the adhesion of a MoN and a TiC PVD coating deposited on steel substrate are introduced. The mechanical properties of the coatings and their steel substrates were determined via nano-indentations and a FEM supported evaluation of the obtained results. The coatings' adhesion and fatigue were quantified by inclined and perpendicular impact tests respectively, coupled with appropriate finite elements method (FEM) calculations. The inclined impact tests were conducted under lubricated conditions for avoiding abrasion caused by sliding friction on the coated surfaces. In this way, the coating fatigue failure during this test was mainly affected by the impact load, the film adhesion and the material's properties. Based on these results, the coating adhesion was estimated considering the impact loads and the determined material properties. [ABSTRACT FROM AUTHOR]

During the Future Advanced Rotorcraft Drive System (FARDS) program, the Aviation Development Directorate (ADD), Aviation Applied Technology Directorate (AATD), Bell Helicopter Textron Inc., University of Toledo and the Aristotle University of Thessaloniki worked together to perform bearing coating tests. The mechanical properties of the DLC coating and its steel substrate were determined via nano-indentations and a FEM supported evaluation of the obtained results. The coating fatigue and adhesion were quantified by perpendicular and inclined impact tests respectively, coupled with appropriate finite element method (FEM) calculations. The inclined impact tests were conducted under lubricated conditions for avoiding abrasion caused by sliding friction on the coated surfaces. In this way, the coating fatigue failure during this test was mainly affected by the impact load, the material's properties and the film adhesion. The effects of these factors on the coating fatigue failure were described via an iterative FEM supported method. Using this method, the coating adhesion was estimated taking into account the exercised impact loads and the determined material properties. [ABSTRACT FROM AUTHOR]

Nano-impact test is a reliable method for assessing the brittleness of PVD coatings with mono- or multi-layer structures. For the analytical description of this test, an axis-symmetrical Finite Element Method (FEM) model was developed using the LS-DYNA software. This software was adequate to simulate the progressive superficial coating fracture induced by the repetitive nano-impacts during the nano-impact test. The coating possesses one or more individual layers with own mechanical properties, since every layer after its deposition at the PVD process temperature is exposed to an annealing affecting its strength data. The annealing duration of each layer is associated with the rest time, up to the deposition of the overall coating thickness. For simulating this procedure and estimating the related mechanical properties of the coating layers, cemented carbide specimens with the same TiAlN PVD (Physical Vapor Deposition) coating of various thicknesses and structures were annealed in vacuum. The annealing duration was equal to the deposition time required for coating a specimen with a further layer up to a constant overall thickness. The superficial strength properties of these coatings were determined via nano-indentations, coupled with FEM calculations to estimate the corresponding stress–strain curves. Results obtained by the developed FEM model simulating the nano-impact test were compared with experimental ones. Taking into account the sufficient convergence between them, the introduced numerical procedure can be effectively employed to evaluate the effect of various coating structures on their brittleness. [ABSTRACT FROM AUTHOR]

The paper aims at clarifying whether thick HPPMS (High Power Pulsed Magnetron Sputtering) PVD coatings can be used more effectively in cutting processes compared to thin ones. In this context, nano-structured multilayer HPPMS PVD coatings with diverse thickness were deposited on cemented carbide inserts of the same specifications. The deposition of multilayer PVD coatings instead of mono-layer ones on cemented carbide tools contributes to a significant improvement of the coated tool life due to their capability to prevent the crack propagation. The coating's mechanical properties and their gradation versus the film thickness were determined by analytical results' evaluation of nanoindentations on annealed coated specimens. The films' brittleness was assessed by nano-impact tests. The strain rate-dependent fatigue endurance of the applied coatings was determined by means of impact tests with modulated force signals, resembling the developed ones during milling. The coated inserts were used in milling hardened steel. A Finite Elements Method (FEM) simulation of the contact between the coated tool and the workpiece provided information for elucidating the effect of the film thickness on the tool wear evolution. These investigations revealed that via increasing the film thickness the tool life is prolonged almost proportionally with the coating thickness augmentation, thus compensating for their higher cost compared to thin coatings. [ABSTRACT FROM AUTHOR]